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Infanticide in higher mammals - Comments

VrijVlinder's Avatar Comment 1 by VrijVlinder

Yes I have also found that aspect difficult to accept. Why kill progeny at all ? The most simple reason can be that the genetics of the new male are superior to the one displaced.

Sun, 01 Jul 2012 20:16:32 UTC | #948401

Carl Sai Baba's Avatar Comment 2 by Carl Sai Baba

There isn't any species-level survival function necessary. A "species" is just a set of genes.

The murderous male's genes are "superior" by evolutionary definition (i.e., better at passing on). And the general existence of whatever species is serving as the premise of this thought experiment only exists because each member had ancestors which also were able to pass on their genes.

Step-father infanticide is not the thing that is hard to explain. The cases which require explanation are the members of a species which behave in ways not directly related to their personal reproduction.

Sun, 01 Jul 2012 20:25:40 UTC | #948402

Carl Sai Baba's Avatar Comment 3 by Carl Sai Baba

One of Robert Sapolsky's videos had a lot of descriptions of the various situations in which the mother, father, or someone else is more likely to kill a baby. I can't remember which one.

Sun, 01 Jul 2012 20:38:08 UTC | #948406

VrijVlinder's Avatar Comment 4 by VrijVlinder

It happens in humans too. Although it is more premeditated in humans. Women have killed their own children to gain another male's affection. I am sure in the case with humans, genetics has no part because these decisions were made intellectually and are not innate functions of a human. Males have also killed stepchildren.

Every time a male gets killed, the genes of that lineage begin to disappear from the gene pool. I think that was the idea when kings etc ordered the killing of all the male babies. From the outside this would look as a way to prevent a group of people from producing warriors in the future. But the greater repercussion is the loss of genetics from that group of people. They likely did not think in terms of genetics but the result is the same.

Decreased variability in the gene pool.

Sun, 01 Jul 2012 20:55:36 UTC | #948409

logicophilosophicus's Avatar Comment 5 by logicophilosophicus

I remember RD discussing this sort of issue in The Selfish Gene - I think the example was swallow chicks, cuckoo-style, tipping the odd sibling (in the egg) out of the nest, and no doubt the lion cub business was mentioned. The key point was that your own species are your most direct competitors.

I always linked that in my mind with JBS Haldane's essay in which he candidly decribed how much he had enjoyed servic in World War I, and Will and Ariel Durant's observation that in several thousand years of human history only 27 had no (recorded) war. Our genes got us here, but we don't always have to approve of their promptings.

Sun, 01 Jul 2012 21:58:31 UTC | #948413

raytoman's Avatar Comment 6 by raytoman

It makes sense for some solitary animals, since they are driven to procreate by their genes, to maximise mating chances. An unprotected female is best, next best an unprotected female with young cubs you can kill to make her receptive to you.

Apes however are not solitary and the tribe typically collaborates to protect and rear all their young.

Some people believe (says so in their Book) that you have the right to kill a man, his wife, his kids and all his animals if he offends you but then they are religious and therefore irrational and without morals.

Sentient animals have evolved brains that enable them to learn and pass on knowledge and develop additional synapses.

Unfortunately, religion typically removes the will/need/opportunity to learn and they are ruled by primitive rules, invented originally in antiquity. The more recent inventions are more geared around creating wealth for the inventers, creating communes where the leaders can have as many young wives as they want and can reward their mates by ordering young girls to marry them or, in the case of one of the older religions, recruit only unmarried men as Priests and protect them from prosecution for paedophilia.

With so few atheists, we may never know how humans would naturally behave towards women and children in comparason to the other sentient creatures.

Currently we are allowing tens of millions of children to starve to death or die of unnecessary diseases, we devote much of our time, energy and wealth in devising, improving and using weapons to kill other humans and we wage religious wars at the drop of a sermon which demonises whole communities in the name(s) of our god(s).

Maybe lions and bears (and their genes) aren't so bad after all (compared to us)..

Mon, 02 Jul 2012 00:29:05 UTC | #948416

Neodarwinian's Avatar Comment 7 by Neodarwinian

http://richarddawkins.net/articles/646363-ucla-biologists-reveal-potential-fatal-flaw-in-iconic-sexual-selection-study

I wonder if these people could find a " fatal flaw " in this fact of mammal infanticide. This sexual selective technique rather guarantees the male genetic make up being passed in mass and preferentially.

Mon, 02 Jul 2012 01:22:02 UTC | #948418

Red Dog's Avatar Comment 8 by Red Dog

I can see where a selfish gene would cause such behavior but it is also very much anti life and anti survival of the species.

You need to read or re-read The Selfish Gene because you haven't grasped the essential concept of the book. There is no such thing as survival of the species much less valueing life for the sake of life, its all a matter of genes which are carried by inividuals. If anything its surprising that there aren't more examples of infanticide. My guess is that the reason there aren't is the risk of false negatives, thinking that a child is not your kin and killing it by mistake as a result is the worst mistake you can make from the standpoint of evolution.

Are the selfish gene and survival of the species working at cross purposes here?

No, because there is no such thing as survival of the species, except possibly for some lower life forms such as ants and bees, see the recent discussion on group selection.

Perhaps I'm wrong but I also sense you may be commitning the naturalistic moral fallacy with your statements about "testosterone soaked males... fill their wild oats" Yes, its offensive to our human morality, that is why Dawkins, Harris, and most people who understand evolution are clear that it is in no way a basis for human morality. By the standpoint of evolution rape is totally logical for males. That is one of many reasons we don't look to evolution for a definition of human morality.

Mon, 02 Jul 2012 01:48:31 UTC | #948421

VrijVlinder's Avatar Comment 9 by VrijVlinder

@Comment 6 by raytoman: Apes however are not solitary and the tribe typically collaborates to protect and rear all their young.

One must not assume all primates are non infanticidal .

Infanticide Sexual selection hypothesis

Infanticide is a male reproductive tactic: Loss of suckling infant leads to the onset of estrous in the mother Males gain a reproductive advantage through earlier conception by females.

Some examples from chimps- when a new female with an infant comes into the group, usually the infant will be killed by the males in the group. As a result, soon the female is in estrous again, which she wouldn't have been for years- and so one of the males in group can have a child by her.

The majority (67%) of all infanticides occur in one-male groups Most (21 or 91%) were committed by strange males 17 (74%) were committed by immigrant males 4 (17.4%) were committed by extra-group males Only 2 (< 10%) were committed by a male within the social group, but in both cases it was a male who had just increased his dominance rank. This is significant because only a higher-ranking male can benefit from a female coming into estrous sooner. 13 cases (=57%) occurred after takeovers by males All 23 of the infant victims were still unweaned

Predictions of high population density hypothesis

Infanticide occurs as high population densities Infanticide will not necessarily benefit the killer

When you plot data matching infanticide occurrences and the population densities, the data points are pretty scattered. However, when you separate them out by one-male groups and multi-male groups, you see that infanticide is a lot more common in one-male groups than in multi male groups. This is consistent with the sexual selection hypothesis because it's the males coming into the groups who are doing the killing when they take over.

Predictions of sexual selection hypothesis

Infanticidal males will not typically be the fathers of the offspring killed Mothers will become sexually active earlier than if their infants had lived Infanticidal males benefit reproductively by killing offspring

Prediction 1- relatedness of infanticidal males an infant victims

In 22 of 23 cases, the infanticidal male was not the probable father because: he was not in the group at the time the infant victim was born; he was sexually immature; or he was of low rank and probably did not father in the infant.

There are no verified cases of a father killing his offspring.

Prediction 2- the effect of infanticide on interbirth intervals

Note that there are two reasons why a male would want to have the females in estrous quickly- one is just to have more kids in his lifetime. The second thing to consider is that he is going to get overthrown sometime too, so he needs to get kids started early so they're weaned by the time some new male comes in so the new guy doesn't kill them.In four cases where data exists, infanticide shortened the interbirth interval by 66%.

Prediction 3- reproductive benefits derived by infanticidal males

In 8 of 21 cases the infanticidal male mated with the mother after killing her infant Males may have sired subsequent offspring in 7 of 14 births following committing infanticide.

Response of females to infanticidal attacks

What do the females have to say about all this? This guy comes and kills their kid and then wants to mate with them! Why would they put up with it?!

The answer is, they're kind of stuck between a rock and a hard place, being in one male groups. If a female doesn't mate with the new guy, then she decreases her own reproductive success. Females who hold a grudge and don't mate are thus selected against, so females who forgive an forget end up having more kids.

Also, if you mate with the guy who killed your baby, then you know that your future sons will have good genes for getting mates for themselves when they grow up and take over a group.

Data from gorillas: When a usurper comes in and kills a female's baby, even though the silverback was trying to save it, females are more likely to leave the old guy and go with the new guy! This new guy has shown how tough he is, and the guy who tried to protect her obviously wasn't able to do it, so she may as well go with the tougher guy and get his tougher genes for her future kids.

Females do have some ways of responding to this threat to their reproductive success. Although refusing to mate won't really work, there are things they can do.

Female coalitions One is to form a coalition of females against the infanticidal male. In some cases, this method is effective and together they can protect their babies from the males- see description in CP. This happens in langurs, redtails, and blue monkeys. Note that they are all matrilineal species, so females are living with relatives.

Help from the males A-- male defense in patrilineal societies In these female-dispersing species, you don't tend to see coalitions between females- but if there are multiple males in the group they will form coalitions to try and protect the babies against potentially infanticidal males. For instance, a new male who has just joined and couldn't have fathered any of the offspring, or else a male who has just risen up in the hierarchy and hadn't mated before so wasn't anyone's father. (Although if he's related to other males who have mated, then he wouldn't be as likely to commit infanticide.)

B-- male-female coalitions: baboons When a new male joins a group, he wants to (well really his ancestors have been selected to) kill the babies, but a female and the guy who was likely to have fathered her baby will join together to protect the infant. Sometimes they're effective and sometimes they're not, but it seems when the male tries to help, they are more likely to be successful in protecting the infant. This could be why there's less infanticide in multi male groups.

Post-conception estrus and promiscuity This is not necessarily a conscious deception- it's just a behavioral trait that has been selected for.

Sometimes when a male takes over a group and begins attacking, pregnant females will extend estrous or even come back into estrous even though there's no way they could possibly conceive- he copulates with them when when she later has an infant he figures it's his and so doesn't kill it. This has been documented in colobines, including langurs and red colobus. Females will extend estrous longer into their pregnancy, and they will copulate a lot more, especially with the new male.

Outstanding problems

This doesn't fit into the picture very well, but it's about chimps. All infanticide we've spoken of so far was committed by males, and this is the rule in primates and other animals. There are some exceptions, and one was documented by Jane Goodall.

A female named Passion began killing and eating several of the babies in her community. Together with her daughter Pom, over a period of many years they attacked and killed infants in their group. Usually when males kill a baby, they don't eat it, but these females seemed to be after meat; they'd chase and consume the infant. They were actually seen to eat 3, chase 3 others, and there were 8 others who disappeared under mysterious circumstances. In this period, there were almost no infants weaned successfully.

So this is kind of a question mark because it's only been these two individuals documented- and the daughter probably learned it from the mom- so maybe we can label this one pathological and say that it's not a part of normal chimp behavior.

But infanticide is.

Mon, 02 Jul 2012 02:03:44 UTC | #948422

Red Dog's Avatar Comment 10 by Red Dog

Comment 1 by VrijVlinder :

Yes I have also found that aspect difficult to accept. Why kill progeny at all ? The most simple reason can be that the genetics of the new male are superior to the one displaced.

No. Animals have no notion of whose genes are "superior" to anothers. Its not even clear how you would measure that. Is a gene for enhanced intelligence "superior"? Probably, but what if it also requires the animal to eat twice as much to feed the enhanced brain or what if (to bring it down to human terms) it makes the male such a nerd that its much harder for him to find a female to procreate with? From the standpoint of evolution killing progeny that are not your kin in order to give your kin or potential kin a better chance of surviving and procreating makes perfect sense. There is nothing controversial or hard to understand, its all a matter of selfish genes.

Mon, 02 Jul 2012 02:06:21 UTC | #948423

VrijVlinder's Avatar Comment 11 by VrijVlinder

I did not want it to mean I felt they had a conscious idea on genetic distributions, that is silly of course they are not aware that is evolution and that the new guy's "genes"are better. However there some innate responses to wanting their ability to continue procreating with what would seem as a better more qualified male that the father of the infant that was killed..

Mon, 02 Jul 2012 02:25:52 UTC | #948425

VrijVlinder's Avatar Comment 12 by VrijVlinder

@RED:the male such a nerd that its much harder for him to find a female to procreate with?

Yes I have heard that from many nerds. It poses a problem if the nerd gene is necessary for analytical intelligence...

Animals have no notion of whose genes are "superior" to anothers.

I could swear some humans do ;)

There is nothing controversial or hard to understand, its all a matter of selfish genes.

Does not mean I can't find it hard to accept in an emotional sense. But I do understand it intellectually .

Mon, 02 Jul 2012 02:49:58 UTC | #948428

ccw95005's Avatar Comment 13 by ccw95005

Think of it this way. Say that a male individual has a mutation which promotes infanticide of other males' offspring. Because that female mother becomes fertile more quickly, the killer has a better chance of impregnating her and carrying his genes forward than if she were still nursing. Evolution works by increasing the frequency of particular mutations in the general population, and it does this by increasing the progeny of those individuals carrying the mutation - either by improving survival or, as in this case, by improving his ability to generate babies.

Remember, evolution doesn't care about improving the species, or ensuring its survival. In fact, evolution doesn't have any intelligence or emotions - although it seems as if it does, sometimes. It's all in the mechanism that Darwin described in his theory.

Mon, 02 Jul 2012 05:53:58 UTC | #948433

Jumped Up Chimpanzee's Avatar Comment 14 by Jumped Up Chimpanzee

Comment 1 by VrijVlinder

Yes I have also found that aspect difficult to accept. Why kill progeny at all ? The most simple reason can be that the genetics of the new male are superior to the one displaced.

Probably the main reason why males kill the offspring of other males of the same species is that there are limited resources available to the raising of offspring, so if a male gets rid of another male's offspring it enhances the chances of survival for his own offspring. Therefore, males that are adept at doing this will have more offspring that in turn will have similar genes driving them towards the same behaviour and so it continues.

Mon, 02 Jul 2012 10:18:50 UTC | #948451

VrijVlinder's Avatar Comment 15 by VrijVlinder

Yes I think I made that clear in Comment 9 by VrijVlinder that other things are at play besides limited resources. read that and tell what you think.

Mon, 02 Jul 2012 10:37:41 UTC | #948453

ColdThinker's Avatar Comment 16 by ColdThinker

Infanticide is an excellent example why darwinism should be understood as a fact of nature, not as a model by which we should behave ourselves. Failing to make this distinction has a lot to do with the popularity of creationism (belief that accepting evolution  leads to accepting immorality) and even a lot of non-creationist right wing thinking (social darwinism). The natural order of things isn't necessarily good or desirable.

Although the mechanics are theoretically beautiful, in real life darwinism is ugly, brutal and horrible. Even though we and the diverse life around us is the product of it, darwinistic evolution is the cruellest game in the universe by any human standard. It should be studied, understood and overcome whenever necessary.  

Mon, 02 Jul 2012 15:12:35 UTC | #948459

nick keighley's Avatar Comment 17 by nick keighley

Comment 1 by VrijVlinder :

Yes I have also found that aspect difficult to accept. Why kill progeny at all ? The most simple reason can be that the genetics of the new male are superior to the one displaced.

The most simple reason is a gene for killing other males' children is that you get to have more children. So the child-killijng-gen tends to increase in the poulation. There are no "superior genes" except in the judgement of natural selection.

Even "higher naimals" don't acuallyread books on ethics or species survival.

Have you read "The Selfish Gene"?

Mon, 02 Jul 2012 15:32:55 UTC | #948461

nick keighley's Avatar Comment 18 by nick keighley

Comment 7 by Neodarwinian :

http://richarddawkins.net/articles/646363-ucla-biologists-reveal-potential-fatal-flaw-in-iconic-sexual-selection-studyI wonder if these people could find a " fatal flaw " in this fact of mammal infanticide. This sexual selective technique rather guarantees the male genetic make up being passed in mass and preferentially.

only when male lions learn to clone themselves. Presumably the lioness manages to rear a brood toyoug adulthoodsooner or later and they are going to be 50% her DNA no matter who the father was!

Mon, 02 Jul 2012 15:37:00 UTC | #948462

nick keighley's Avatar Comment 19 by nick keighley

Comment 8 by Red Dog :

No, because there is no such thing as survival of the species, except possibly for some lower life forms such as ants and bees, see the recent discussion on group selection.

even ants and bees have genetic reasons for what they do. Look up ant genetics. Notice also, not many groups of insects locked onto this particular mode of living.

Mon, 02 Jul 2012 15:40:14 UTC | #948463

Alan4discussion's Avatar Comment 20 by Alan4discussion

Comment 18 by nick keighley

only when male lions learn to clone themselves. Presumably the lioness manages to rear a brood toyoug adulthoodsooner or later and they are going to be 50% her DNA no matter who the father was!

Presumption is a usual cause of errors. Research is required.

Lionesses are in most circumstances unlikely to raise more than the odd cub at best, outside of a pride where cooperative hunting acquires food. Even in prides, large numbers of cubs die young.
Prides are usually made up of a group of lionesses, with (about) two dominant male lions fathering all the cubs. The males guard the pride's hunting territory from other lions. It is usual for new lions taking over a pride after defeating the previous dominant males, to kill any cubs fathered by the defeated males, thereby bringing the lionesses back into season to mate with them.

Mon, 02 Jul 2012 18:58:44 UTC | #948466

Neodarwinian's Avatar Comment 21 by Neodarwinian

@ nick keighley

No male lion needs to clone himself when all he has to do is kill the cubs of another male lion. I thought it too obvious to mention the 50-% constant female contribution to the genetic mix.

Some male lions will reign longer than others and the longer rulers will have the greater amount of descendents, while some male lions may have no descendents as their first and only born will be victims of infanticide.

No female input needs be considered here and that was the point. No cloning needed, just this sexual selective technique.

Mon, 02 Jul 2012 20:28:00 UTC | #948470

VrijVlinder's Avatar Comment 22 by VrijVlinder

if human males could clone themselves, I must conclude that the gene pool would get very small and eventually those people would die off.

Cloning is only practical in cell divisory organisms. Protozoa , bacterium, etc. Cutting an earthworm in half could constitute cloning.

The closest thing to cloning in organisms that are hermaphrodites with two sets of sex organs , male and female. Auto insemination.

One can't get away from ovum and fertilization after that.

Mon, 02 Jul 2012 20:47:18 UTC | #948472

raytoman's Avatar Comment 23 by raytoman

On Cloning,

Only females can clone themselves - the have the eggs and the DNA. Males only have the DNA.

How long I wonder before women wise up and do just that.

Tue, 03 Jul 2012 00:15:52 UTC | #948475

CEVA34's Avatar Comment 24 by CEVA34

"Are the selfish gene and survival of the species working at cross purposes here?"

Why is that idea surprising? Obviously the "behavior" of genes sometimes runs contrary to the survival of the species, otherwise all those extinct species wouldn't be extinct! Of course that excludes species exterminated by outside forces like climate.

Tue, 03 Jul 2012 08:25:14 UTC | #948486

Alan4discussion's Avatar Comment 25 by Alan4discussion

Comment 24 by CEVA34

"Are the selfish gene and survival of the species working at cross purposes here?"

Why is that idea surprising? Obviously the "behavior" of genes sometimes runs contrary to the survival of the species, otherwise all those extinct species wouldn't be extinct! Of course that excludes species exterminated by outside forces like climate.

Is this not more in line with the selfish genes guiding the survival of the species?

The ecosystem will only support a certain number of lions, so the surviving cubs will be the ones of the fathers who were there supporting them and maintaining their mothers' hunting territory.

The selfish genes of new dominant males, are not going to waste their time and efforts bringing up the cubs of the previous males, delaying and diverting resources from gene copies in their own offspring!

Tue, 03 Jul 2012 10:57:36 UTC | #948488

nick keighley's Avatar Comment 26 by nick keighley

Comment 22 by VrijVlinder :

my tongue-in-cheek remarkwas addressed tothe person who thought a male committing infanticide would cause male genes to predominate. With a sexualreproducing species female genes cannot be removed from the gene pool

if human males could clone themselves, I must conclude that the gene pool would get very small and eventually those people would die off.Cloning is only practical in cell divisory organisms.

cf. Dolly The Sheep etc.

Protozoa , bacterium, etc. Cutting an earthworm in half could constitute cloning.

I'm not sure this is true. Plants clone quite easily

The closest thing to cloning in organisms that are hermaphrodites with two sets of sex organs , male and female. Auto insemination.One can't get away from ovum and fertilization after that.

I don't think hemaphodites usually have sex with themselves (though there is some pretty strange stuff in nature).

Cloning also happens with parthenogensis (females giving birth without sex) amny animals do this including quite "high order ones" such as lizards.

Tue, 03 Jul 2012 12:45:13 UTC | #948494

Neodarwinian's Avatar Comment 27 by Neodarwinian

@ nick keighley

Particular male genes.

Thought I would clear that up though I thought my second post was rather clear on that point.

" cause male genes to predominate. " Makes little sense in sexually reproductive organisms with sex linked traits and a XX, XY gamete distribution. Still, averaged out over many children certain males would be better represented than others with some not represented at all.

Tue, 03 Jul 2012 19:31:24 UTC | #948518

LaurieB's Avatar Comment 28 by LaurieB

VrijVlinder,

I always found it disturbing to watch the nature shows where the male lions would come charging in and kill the adorable cubs. The violent chimps were a little too close to home and therefore even more disturbing. But what really choked me was when I read the book Mother Nature, by Sarah Hrdy where she describes in detail infanticide by human females. That was the last straw for me. Although I could pass scornful judgement on lions and chimps, I couldn't fathom why a human female would destroy her own offspring. At that moment, for me, that's when I accepted that we are only apes; only animals; not special.

Tue, 03 Jul 2012 20:06:41 UTC | #948520

VrijVlinder's Avatar Comment 29 by VrijVlinder

@LaurieB: At that moment, for me, that's when I accepted that we are only apes; only animals; not special.

Yes that realization however intellectually understood, is something humans have been trying to eradicate from human nature. Is it possible to reach a point where pathological behavior such as this, is ousted from human behavior?

If so what would it take, how long would it take ? would it spell the end of the human race?

That saying "Nature is wise", is this what it means? If things are the way they should be according to nature, who are we to interfere or change the path of evolution a certain species should take?

I think humans are more than apes. They are a plague. No amount of infanticide in humans will change that. Every second a new baby is born. At this rate we will no longer be able to maintain support of all the people. In China they have a child limit or people pay fines or worse. This may seem as inhumane but infanticide or forced sterilization is much worse.

In the case of humans, this behavior will not be focused only on infants. If resources are at stake humans will kill each other. That is nature.

Tue, 03 Jul 2012 22:41:20 UTC | #948526

VrijVlinder's Avatar Comment 30 by VrijVlinder

@Comment 26 by nick keighley: I'm not sure this is true. Plants clone quite easily

Indeed, but this thread is about higher primates not cross pollination or genetically mutated corn....

I recommend a great read about this in a novel by DR Robin Cook called Chromosome 3. I love these novels because he uses real science in his stories. Kind of an Asimov of Biology.

Tue, 03 Jul 2012 23:02:13 UTC | #948528